Technical Field
The present disclosure relates to a semiconductor device and a semiconductor device control method.
Related Art
As a drive method for a liquid crystal panel including plural segment electrodes and plural common electrodes arrayed in a lattice formation, a matrix drive method is known in which common electrodes are selected in sequence by applying a scanning voltage sequentially to the plural common electrodes, and a signal voltage is applied to the segment electrodes connected to the pixels desired to be switched ON, from out of the pixels connected to the selected common electrode. Moreover, a 1/S bias drive method is known in which the level of voltage applied to the common electrodes and the segment electrodes is changed in plural steps. Known technology related to a liquid crystal drive circuit for driving a liquid crystal panel using such a drive method includes the following example.
For example, Japanese Patent Application Laid-Open UP-A) No. 2013-41029 describes a liquid crystal drive circuit including a common signal output circuit that supplies a common signal taking, in a predetermined sequence, a first potential, a second potential, or an intermediate potential, to common electrodes of a liquid crystal panel, and including a segment signal output circuit that supplies a segment signal taking, according to the common signal, a first potential, a second potential, or an intermediate potential, to segment electrodes of the liquid crystal panel. In such a liquid crystal drive circuit, the segment signal output circuit increases the impedance of the segment signal only for a first period when the segment signal output circuit is switching the potential of the segment signal.
In a case in which a liquid crystal panel is driven by 1S bias, the voltage levels of the common voltage applied to the common electrodes and of the segment voltage applied to the segment electrodes are changed in (S+1) steps. Thus in a liquid crystal drive circuit that drives the liquid crystal panel using 1/S bias driving, the voltage level of output voltage is appropriately changed in a power source section that outputs a power source voltage for generating the common voltage and the segment voltage.
However, it is known that in a liquid crystal panel, in a case in which unevenness occurs in the direction of the electrical field applied to the liquid crystal elements, the liquid crystal elements deteriorate under the action of electrolysis and the like. Thus in a liquid crystal drive circuit, in order that unevenness does not occur in the direction of the electrical field applied to the liquid crystal elements, frame inversion is performed in which the magnitude relationship between the voltage applied to the common electrodes and the voltage applied to the segment electrodes is inverted between a front half period and a rear half period of a single frame, while pixels maintain a switched ON state.
A power source section of a liquid crystal drive circuit that drives a liquid crystal panel using a 1/S bias drive method switches the voltage level of the output voltage during frame inversion. Switching the output voltage of the power source section is performed, for example, by employing plural switches provided between each of the power source lines of mutually different voltage levels, and the output terminal. However, shoot-through current flows between the power source lines in a case in which a period arises in which plural of the switches adopt an ON state at the same time. Disruption to the voltage levels of the common voltage and the segment voltage arises as a result, and abnormal display, such as flickering, may be generated in the liquid crystal panel. In order to prevent the generation of such shoot-through current, a timing regulation circuit is employed so as to switch a switch connected to one power source line ON, only when the switch connected to another power source line has been switched OFF.
However, due to recent demands for lower voltages for semiconductor devices, it is becoming difficult to completely prevent the generation of such shoot-through current using a timing regulation circuit. Namely, in cases in which the power source voltage supplied to a semiconductor device has been lowered, the lag time caused by the slew rate, the wiring line length, and the capacity load etc. of the circuit formed by the semiconductor device becomes significant, and either the timing regulation circuit ceases to function appropriately, or the circuit does not operate at the intended timing due to the influence of the lag time generated in at a stage after the timing regulation circuit.
To address this issue, conceivably circuit simulation could b employed to design a circuit that takes into consideration the influence of lag time when at low voltage. However, the precision of circuit simulation is low in low voltage regions (for example, 1V or lower), requiring considerable man-hours and cost for validation operations on the circuit design. Due to lowering the voltages of semiconductor devices, it is accordingly difficult to prevent the generation of shoot-through current in a liquid crystal drive circuit, and there is a need for new technology to suppress the generation of abnormal display caused by shoot-through current in a liquid crystal panel.